Bulked nonwovens

ABSTRACT

A PROCESS WHICH COMPRISES EXTRUDING A SOLUTION OF A LOWER ALKANOIC ACID ESTER OF CELLULOSE TO FORM FILAMENTS, MOVING THE FILAMENTS ABOUT WHILE IN A MUTUALLY ADHESIVE CONDITION TO CAUSE THEM TO BECOME RANDOMLY DIRECTED AND BONDED TO ONE ANOTHER AT SPACED POINTS, COLLECTING THEM IN A FORM OF A BONDED NON-WOVEN WEB AND CONTACTING THE NON-WOVEN WEB WITH STEAM TO THEREBY IMPROVE THE PHYSICAL PROPERTIES OF THE WEB, I.E., COVERING POWER, RESILIENCE, INSULATION, STRENGTH, DENSITY AND HAND.

3,669,788 BULKED NONW OVENS William T. Allman, Jr., Ashland, Va., andCharles W.

Joseph, Rock Hill and Ralph G. Higgins, Jr., Spartanburg, S.C.,assignors to Celanese Corporation, New York, N.Y.

No Drawing. Continuation-impart of application Ser. No.

558,177, Mar. 15, 1966, which is a division of application Ser. No.266,123, Feb. 20, 1963, which in turn is a division of application Ser.No. 778,248, Dec. 4, 1958, now Patent No. 3,100,328, dated Aug. 13,1963. This application Oct. 10, 1969, Ser. No. 870,385

Int. Cl. D04h 3/16 U.S. Cl. 156-167 4 Claims ABSTRACT OF THE DISCLOSUREA process which comprises extruding a solution of a lower alkanoic acidester of cellulose to form filaments, moving the filaments about whilein a mutually adhesive condition to cause them to become randomlydirected and bonded to one another at spaced points, collecting them ina form of a bonded non-woven web and contacting the non-woven web withsteam to thereby improve the physical properties of the web, i.e.,covering power, resilience, insulation, strength, density and hand.

This application is a continuation-in-part of copending application Ser.No. 558,177, filed Mar. 15, 1966 now abandoned, which is a division ofapplication Ser. No. 266,123, filed Feb. 20, 1963 now abandoned, whichin turn is a division of application Ser. No. 778,248, filed Dec. 4,1958, now US. Pat. 3,100,328 issued Aug. 13, 1963.

The present invention relates to novel nonwoven articles characterizedby high bulk and a soft hand.

It is an object of the invention to provide nonwoven filamentarymaterials of increased covering power, resilience, insulation andstrength as well as of softer hand.

Other objects and advantages of the invention will become apparent fromthe following detailed description and claims.

In accordance with one aspect of the present invention, a nonwovenarticle comprising organic acid ester of cellulose filaments bonded toone another at spaced locations is subjected to steaming whereby thephysical properties of the article are changed, viz. the covering poweris increased along with the resilience, insulation and strength whilethe density is decreased and the hand is improved.

The steaming is advantageously carried out at a temperature ranging fromabout 95 to 180 C. and preferably 110 to 125 C. The pressure isgenerally superatmospheric but atmospheric or even reduced pressure mayprevail.

The duration of the steam treatment will depend upon the temperature andupon the thickness and construction of ,the article being treated.Generally it will be at least about 1 minute to produce a substantialimprovement and it may be as long as 10 minutes or more. At thepreferred temperatures the duration of steaming is preferably about 1 to5 minutes.

The nonwoven article may comprise a web, fleece or sheet materialcomposed of staple length fibers either randomly disposed or oriented toa greater or lesser deg'ree as by carding, the fibers being bonded toone another at spaced points.

y In accordance with another aspect of the invention, the nonwovenarticle comprises a web, fleece or sheet material composed ofsubstantially randomly directed substantially United States Patent 0continuous filaments bonded to one another at spaced points of contact.Advantageously such webs may be formed as described in detail inapplication Ser. No. 744,844 filed June 26, 1958, now US. Pat. 3,148,101issued July 16, 1964.

Briefly, filament-forming material in liquid phase is extruded through aplurality of orifices to form continuous filaments which may beagitated, such as by blasting with air, while still mutually adhesive,to cause them to swirl about and coalesce randomly. The filaments arecontinuously drawn away from the extrusion location in the form of anonwoven web or fleece. As the web dries, the filaments become bonded toone another. The web so produced can be directly steamed or it may besubjected to intermediate treatments such as hot calendering to increasethe number of points of fusion and the density. Various adsorbents,pigments, etc. can be incorporated in the nonwoven either by being addedto the dope which is being spun or by being deposited on the web asformed.

The denier of the individual filaments of the nonwoven may vary withinwide limits, e.g., from less than 1 up to 20 or more, althoughpreferably it ranges from about 2 to 16. The weight per square yard ofthe nonwoven can also vary widely, depending upon its thickness,density, etc.

The filamentary material may comprise an organic acid ester of cellulosesuch as cellulose acetate, cellulose propionate, cellulose butyrate,cellulose acetate propionate, cellulose acetate butyrate, or the like.The esters may be triesters, i.e. esters containing fewer than about0.29 free hydroxyl groups per anhydroglucose unit of the cellulosemolecule, or they may be conventional secondary or ripened esterscontaining about 0.6 free hydroxyl groups per anhydroglucose unit. Thenonwoven articles may comprise mixtures of these filamentary materialswith each other or with other filamentary materials either natural orsynthetic, e.g., cotton, wool, silk, rayon, nylon, polyethyleneterephthalate, acrylics, polyolefins, polymers of halo-olefins such asvinyl chloride or vinylidene chloride, etc.

In accordance with another aspect of the invention, the non-wovenarticle may comprise a mixture of continuous filaments of a cellulosetriester and of a secondary cellulose ester, e.g., cellulose triacetateand conventional cellulose acetate. This can be formed by simultaneouslyextruding a solution of cellulose triacetate in methylene chloridethrough one set of orifices and extruding a solution of conventionalcellulose acetate through a second set of orifices. The filaments formedby such extrusions are positioned near each other and a blast of aircauses them all to swirl and entangle with one another, becoming fusedat spaced points as the web dries. Steaming produces exceptionally highbulk because of the effect on the filaments individually as well asbecause of the difierences in the thermal characteristics of thedifferent types of filaments.

While not wishing to be bound thereby, the change in physical propertiesupon steaming is believed due to the following effects: Upon drying offreshly formed cellulose ester filaments, especially of substantiallycontinuous filament nonwovens wherein the filaments are fused at spacedpoints of contact, the filaments undergo compression or other stressesbetween fusion or weld points. During subsequent steaming the stressesare released and the filaments become distorted into sinusoidal, helicalor other threedimensional crimp-like configurations between the welds.In addition, the filaments are somewhat softened and make additionalbonds with adjacent filaments as the expansion creates new points ofcontact. The movement of the filaments increases the interlocking offilaments so that the final structure is stronger, in addition to being"ice less dense as a result of the three-dimensional bulking. At thesame time there is an improvement in the hand of the nonwoven, i.e., itbecomes softer.

In the event that the filamentary material of the nonwoven is initiallymore or less oriented and the nonwoven accordingly much stronger in onedirection than another, the steaming decreases the orientation andreduces the difierential strength.

In spite of their'increased strength and abrasion resistance, theproducts may be completely free of extraneous binders and/orplasticizers.

The steaming treatment can be effected with the nonwoven startingmaterial in sheet form either flat or wound in a roll loosely about ashaft. Alternatively the nonwoven may be in a form approximating thatrequired for an end use, e.g., it may be wound about a perforatedcylindrical core in a form suitable for use as a cylindrical oil filtercartridge. The non-woven may be incorporated as an interlining orfilling material between layers of fabric or the like and the compositearticle may be subjected to steaming. In general, the product will beuseful wherever nonwovens have heretofore found application.

A first solution of filament-forming material, e.g., conventionalcellulose acetate in acetone, is extruded as a plurality of filamentsthrough a spinnerette; a second solution of filament-forming material,e.g., cellulose triacetate in methylene chloride, is extruded through aspinnerette. Blasts of air are directed at the two sets of filamentsthrough nozzles, causing the filaments to swirl about and to contact oneanother while still wet with solvent and in mutually adhesive condition.-As the filaments dry they fuse or. form welds at their contact pointsand deposit on a screen as a randomly directed fleece which leaves thecabinet through an opening defined by a pair of rolls, which preventexcess leakage of solvent vapors from the cabinet. The fleece is takenup loosely on a roll simultaneously with a separating web such as paperunrolled from a supply package. When the roll reaches a predeterminedsize the :fleece and web supplying the roll are cut, the roll is removedand a new roll is started.

The roll of predetermined size is placed in an enclosure and steam isadmitted. After a predetermined time the line is closed to terminate.steaming and relatively cool air is forced in to purge the steam and tocool the roll. The roll is then removed and can be used in conventionalmanner, stripping the paper separator as the roll is unwound.

A nonwoven sheet material composed of substantially continuous filamentsof relatively high denier is very fiat and has a high gloss and stiffhand, the filaments having a plastic rather than a textile appearance.After steaming, the sheet is about twice as thick, the luster is reducedconsiderably and, while still somewhat stifi, the feel is similar tothat-of a starched natural fiber web rather than a plastic. In addition,the individual filaments are characterized by numerous crimps extendingin three dimensions which increase the covering power of the article.

With initially more dense nonwovens the same differences willresult,.but the individual filaments are not as readily identifiable,except on closer observation.

The following example is given to illustrate the invention further:

EXAMPLE A heated dope of cellulose acetate in acetone is extrudedthrough a spinnerette provided with 60 circular orifices each 126microns in diameter. The linear speed of extrusion through the orificesis 3750 meters per minute, and the speed of screen 12 is 75 meters perminute. The denier of the filaments of the nonwoven ranges from about 2to 7 and its weight is 2 ounces per square yard. After autoclaving for 8minutes with steam at 121 C. and :15 p.s.i.g., the nonwoven shrinks inwidth from an. initial value of 4.5 inches down to 4.3 inches. The sheetweighs about 2.1 ounces per square yard and its thickness has increasedfrom about 0.02 to 0.06 inch.

It is tobe understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madeherein without departing from the spirit of our invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The process which comprises extruding a solution of a lower alkanoicacid ester of cellulose to form continuous filaments, moving saidcontinuous filaments about while in mutually adhesive condition to causethem to become randomly directed and to bond to one another at spacedpoints as the filaments dry and collecting them in the form of a dry,bonded nonwoven web, and contacting said bonded nonwoven web with steamat a temperature of from about to C.

2. The process which comprises extruding a solution of a lower alkanoicacid ester of cellulose through a plurality of orifices to formsubstantially parallel continuous filaments, agitating said filamentswhile in mutually adhesive condition whereby they become randomlydirected and bonded to one another at spaced points as the filamentsdry, collecting said filaments in the form of a dry, bonded nonwoven webin which the filaments are substantially continuous, and contacting saidbonded nonwoven web with steam at a temperature ranging from about 95 to180 C.

3. The process which comprises extruding a solution of cellulose acetatein a volatile solvent into an evaporative atmosphere through a pluralityof orifices to form substantially parallel continuous filaments,agitating said filaments with air while in mutually adhesive conditionto cause them to swirl about and entangle, whereby they become randomlydirected and bonded to one another at spaced points as the filamentsdry, collecting said filaments in the form of a dry, bonded nonwoven webin which the filaments are substantially continuous, and contacting saidbonded nonwoven web with steam at a temperature ranging from about 95 to180 C. for at least about 1 minute.

4. The process which comprises extruding through one set of orifices asolution of secondary cellulose acetate to form substantially parallelcontinuous filaments, extruding through another set of orifices asolution of cellulose triacetate to form substantially parallelcontinuous filaments, agitating said filaments while in mutuallyadhesive condition to cause them to swirl about and entangle, wherebythey become randomly directed and bonded to one another at spaced pointsas the filaments dry, collecting said filaments in the form of a dry,bonded nonwoven web in which the filaments are substantially continuousand contacting said bonded nonwoven web with steam at a temperatureranging from about '95 to 180 C.

References Cited UNITED STATES PATENTS 4/1949 Koster 8-l49.3

9/1964 Allman et al. 156-167 U.S. Cl. X.R. 156-481, 306

